Emitted when the IMSI for the connection changes. This sort of thing is rare, but could happen on cellular phones that allow hot-swapping of SIM cards. In the case of SIM swapping, this signal would be emitted twice; the first time while the SIM is being ejected (with an empty string), and the second time after a new SIM has been inserted (assuming that the IMSI can be determined from the new SIM).